The ionic nature of amylase.

Abstract

By studying the distribution of trypsin and pepsin between suspended particles of gelatin and the fluid surrounding them, Northrop 1 has been able to show that these enzymes behave like univalent ions, the former being a cation and the latter an anion. We have carried out some preliminary experiments in which Northrop's procedure has been used to investigate the ionic nature of amylase.

Particles of iso-electric gelatin were suspended in solutions, the pH of which was varied by the addition of HCl or NaOH. On the alkaline side of the iso-electric point a small amount of KCl was added to furnish an ion (Cl^-) which could easily be titrated. The suspensions were stirred constantly for 2 hours. The solution containing the enzyme 2 was then added, and stirring was continued for 2 hours more; the temperature was maintained between 0° and 4° C. The gelatin was then separated from the surrounding fluid by filtration, and the concentration of amylase in the filtrate and in the melted gelatin was determined by a viscometric method. 3

In the accompanying table the ratios of the amylase concentration in the gel to that in the filtrate at various hydrogen ion concentrations are compared with the corresponding ratios of the Cl^- ions 4 in the 2 phases. Since the preparation used contained a small amount of trypsin, the ratios for this enzyme were also determined in a few instances. 5 The figures in the table represent single experiments.

As can be seen from the table, the distribution of amylase between the gelatin and the filtrate is extremely variable from pH 3.8 to 5.6. It would seem that forces other than those of the Donnan Equilibrium play a part here.